AMPK (AMP-activated protein kinase) is an enzyme that functions to control a metabolic pathway so as to maintain balance between supply of nutrients and demand for energy, and thus maintain energy homeostasis in cells and the whole body. AMPK is activated as the ratio of AMP/ATP in the cells increases due to a hypoxemic state or glucose deficiency. The activated AMPK induces fatty acid oxidation to produce a larger amount of ATP and inhibits anabolisms requiring the use of ATP. Also, AMPK activation enhances sensitivity to insulin, inhibits glucose generation in the liver, and improves glucose absorption in the muscles. Due to its actions, AMPK has been regarded as a desirable target for treatment of type II diabetes mellitus and metabolic diseases. AMPK inhibits proliferation of cancer cells and kills cancer cells by regulating energy metabolism in the cancer cells as well as in normal cells. AMPK activated in cancer cells shows an anticancer activity by phosphorylating mTORC1, p53, fatty acid synthase and the like to regulate the cell cycle, cell polarity, autophagy, apoptosis, etc.
Metformin has been used to treat insulin-independent diabetes mellitus (i.e., type II diabetes mellitus) since it is most effective at lowering blood glucose, does not develop hypoglycemia or hyperinsulinemia and can prevent complications among oral therapeutic agents for treating diabetes mellitus. In recent years, metformin has been extensively researched. Also, it was reported that metformin activates AMP-activated protein kinase (AMPK) by inhibiting the action of complex 1 of the electron transport system in the mitochondria to obstruct intracellular generation of energy and inhibits activation of the mTOR/S6K1 signaling pathway in which proteins essential for survival are produced to obstruct proliferation of cancer cells and tumor growth (Mol. Cancer Ther. 9(5): 1092-1099 (2010)). Consequently, metformin has received considerable attention as an anticancer agent for regulating cancer cell metabolism. Also, an epidemiological survey confirmed that the incidence of cancer and mortality by cancer were lowered for patients treated with metformin (BMJ.330: 1304-1305 (2005)).
Meanwhile, there is increasing clinical evidence indicating that cancer stem cells take part in recurrence and metastasis of cancer. The cancer stem cells refer to cancer cells that have self-regeneration or differentiation capacity which is characteristically innate to stem cells. The cancer stem cells are present in the cancer tissue at a content of 0.2% or less, and are characterized by their slow proliferation. Since lots of anticancer agents developed so far target cancer cells that proliferate rapidly, the cancer stem cells are resistant to conventional anticancer therapy when cancer stem cells are treated with the anticancer agents, thereby causing poor prognoses. On the other hand, it was reported that metformin prevents the recurrence of cancer as it selectively acts on cancer stem cells among breast cancer cells and removes the cancer stem cells (Cancer Res. 69(19): 7507-11 (2009)).
Also, it was found that metformin prevents the metastasis of cancer by interfering with the motility and invasion of the cancer cells since it inhibits the expression of Snail 1, Slug, Twist, ZEB 1/2 and TGF-β, which are transcription factors associated with the epithelial-to-mesenchymal transition (EMT), and promotes the expression of E-cadherin to prevent cancer cells from leading to the EMT (Cell Cycle 10: 7, 1144-1151 (2011), Cell Cycle 9: 18, 3807-3814 (2010), Cell Cycle 9: 22, 4461-4468 (2010)).
However, metformin is generally administered three times a day, with a single dose of approximately 500 mg or more. Thus, a tablet that can contain approximately 1,500 mg or more of metformin is required in order to prepare metformin in the form of a sustained released tablet to be administered once a day. In this case, the tablet is too large for patients to swallow. In addition, since one tablet of a sustained-release preparation currently available on the market contains only approximately 750 mg of metformin, two or more tablets of the sustained-release preparation should be taken. Also, the use of phenformin, which belongs to the same group of biguanides, has been completely prohibited since the late 1970s due to its severe side effects such as lactic acidosis.
For these reasons, there is a need for a biguanide-based substance that exhibits better pharmacological action than the conventional metformin and has improved physiochemical properties without the side effects of phenformin.